Almost all buildings include some type of exterior fluid delivery system. The most common outdoor fluid delivery system is comprised of a faucet with a handle for actuating a valve that initiates or ceases fluid flow from a fluid source through a sill cock of the faucet. In order to direct the exiting fluid, it is also well known to employ a hose that is threadingly interconnected to the sill cock. Fluid in the hose may, under certain conditions, enter the faucet and ultimately the fluid source. For example, if the fluid pressure in the hose is greater than the fluid supply pressure Aback flow@ will occur. Such back flow may be harmless. One skilled in the art will appreciate, however, that the fluid in the hose could be harmful and result in spoilage of the water supply or contamination of fluid dispensing apparatus often interconnected to the hose.
One source of contamination includes pesticides and/or fertilizers that are often associated with a delivery system that is interconnected to the open end of the hose. Fluid from the supply is used to dilute those harmful chemicals in the delivery system prior to being distributed. Most municipalities require that a one-way check valve be included in a fluid supply line that delivers water from a public water source to a dwelling so that contaminated water cannot enter the public water supply from the dwelling. Often, there is no requirement that dictates that similar precautions are taken with respect to an exterior fluid delivery system that is associated with a dwelling. It is entirely conceivable that contaminants entering a dwelling from an outside fluid source will affect individuals associated within the dwelling but not the public at large. Further, if the above-mentioned check valve is absent or malfunctioning contaminants could also enter the public water supply via the dwelling.
Another issue related to back flow is the harmful effects of freezing when supply pressure is reduced and/or flow is stopped wherein liquid accumulates within the faucet and/or related plumbing. When the ambient temperature drops, the trapped liquid may freeze potentially causing severe damage to the faucet interconnected check valve and/or associated plumbing. To address this freezing, draining features have been incorporated into prior art check valves, such as the A. W. Cash Valve Company Model VB-111, which includes a stem that must manually be actuated to allow drainage when a hose is not connected. This type of manually draining valve relies on an operator to drain the valve, and is thus not reliable. Self-draining check valves, however, are also known in the art and are disclosed in U.S. Pat. No. 4,712,575 to Lair (ALair I@), which is incorporated by reference herein. Lair I discloses a self-draining, single valve back flow preventor. When a hose is detached, a spool succumbs to spring pressure and moves axially outwardly from the outlet end of the check valve. A valve, housed within the spool, is thus allowed to move axially from its sealing washer to permit drainage. When the hose is connected, the spool and the valve housed therein, are forced axially toward a sealing washer to create a seal that prevents back flow. Vent holes in the check valve prevent accumulation of back pressure within the valve. Sufficient water pressure during supply flow with the hose attached overcomes a spring used to seat the valve and deflects a vent sealing washer, thereby sealing the vent holes. One drawback of the Lair valve is that foreign material may lodge between the valve and the sealing washer, creating a passage through which back flow may occur.
One way to address the major drawback of Lair I is to provide a second check valve. U.S. Pat. No. 3,905,382 to Waterston (AWaterston@), which is incorporated herein, discloses a check valve with two normally closed spring biased valves, one inside an outlet, and the other located near an inlet. The central portion of the Waterston check valve has an externally-threaded vent outlet. When flow occurs, the supply pressure forces the inlet valve axially from its seat toward the outlet and seals the vent. As flow progresses to the outlet valve, the flow pressure compresses an outlet spring and fluid is free to flow from the check valve. When flow ceases and back flow pressure is sufficient to overcome the valve in the outlet, liquid accumulates in the sealed tube and is discharged through a vent.
The Waterston valve does not provide a draining feature that relieves accumulated liquid upstream from the check valve. In the event of freezing the accumulation of liquid upstream from the check valve can result in severe damage to the check valve and plumbing upstream of the check valve. In addition, contamination may collect in the internal portion of the check valve such that when a back flow condition occurs, the contamination trapped in the check valve may enter the fluid supply.
Another system that employs more than one check valve to prevent back flow of a liquid into a distribution system by eliminating pressure differentials that may occur between the faucet and interconnected hose, is the V-444 Valve (AV-444″) manufactured by A. W. Cash Valve Company. The V-444 is succinctly described in U.S. Pat. No. 5,228,470 to Lair et al. (ALair II@). The V-444 employs three separate valves enclosed in a housing that allows drainage of the sill cock after the hose is removed and also prevents backflow into the structure. The V-444 includes an outer housing with an internally situated movable spool. The spool includes an o-ring positioned on an angled upper surface thereof that cooperates with an angled inner surface of the housing to define a first valve that selectively opens and closes an outer passage that allows trapped fluid in the sill cock to drain from a plurality of vent holes. The V-444 also includes an inlet check valve and an outlet valve that controls fluid through the valve and that prevents backflow.
In a first mode of use, wherein no hose is connected and supply pressure is absent, the V-444 is self-draining. A spring forces the spool downwardly to open a fluid path that drains fluid from the sill cock through the plurality of vent holes. Fluid trapped within the inlet and outlet check valves also drains from the outlet of the valve.
In a second mode of use, wherein the V-444 is exposed to supply pressure without a hose interconnected, the spring will force the spool downwardly, thereby creating a path for water to flow through the vents of the check valve. The supply pressure will also deflect the inlet check valve and the outlet check valve so that fluid will be able to exit the valve system.
In a third mode of operation, a hose is interconnected to the outlet portion of the V-444, but no supply pressure is provided. Any back pressure generated by fluid in the hose will force the outlet check valve to seat upon a surface provided by the spool. In this configuration, a hose forces the spool upward, thereby closing the first valve so that any fluid within the inlet check valve on the outlet valve can only travel out of the vents and not into the fluid supply.
In a fourth mode of operation, supply pressure is added to the V-444 with a blocked interconnected hose. Here, fluid from the fluid supply causes a seal to deflect, thereby blocking the vents. In addition, the outlet check valve is seated as described above, thereby preventing fluid from entering into the center of the V-444.
The V-444 includes a fifth mode of operation that is similar to the fourth mode wherein the hose is open to free flow. Again, since the hose is interconnected, the first valve is closed. Fluid pressure causes the inlet valve to transition downwardly to seat on the stem, thereby allowing fluid to flow through the center of the inlet check valve. The fluid pressure also pushes the outlet valve downwardly from its seat on the stem, which allows fluid to freely flow into the hose.
Among the major drawbacks of the V-444 are its size, weight, dimensions and inclusion of components that add to its complexity and expense, thereby rendering it unsuitable for use in various situations. More specifically, the V-444 check valve is approximately 2.2 inches in length and 1.9 inches in diameter and weighs about 200 grams. This size is attributed to the use of complex valving mechanisms and the provision of a first valve that includes a movable spool.
Other back flow preventors have been employed such as those similar to the backflow preventor shown and described in U.S. Pat. No. 7,013,910 to Tripp (“Tripp”), which is incorporated by reference herein. Tripp discloses an in-line backflow preventor that is used in fluid carbonation systems is interconnected between a fluid source and a mixing tank. The pressure in the mixing tank of these systems is often greater than the source pressure. Tripp is designed for either continuous down-steam pressure increases or intermittent down-stream pressure variations. Accordingly, Tripp does not have the capability of releasing pressure upstream of the valve outlet. Further, Tripp, due to its normally closed configuration, does not automatically drain or contain other similar features that are required for freeze prevention.